Usually, when a link is established between two devices, upper protocol layers create logical connections and data contexts associated with these connections. For example, once a Bluetooth link has been created; upper layers such as L2CAP, RFCOMM, BNEP, and TCPIP create logical channels and maintain session contexts. The applications themselves create specific contexts. Contexts of interest are also the security contexts built for message encryption, message integrity, authentication, identification and authorization purpose. Each protocol layer expects a link manager to maintain the link available between said two devices. If the link is lost, they expect to be notified of the link down event.
During periods of inactivity, when there is no transfer of data between the two devices through the link, the link manager periodically sends polling packets in order to have the assurance that the link between the devices is still operational and also to maintain a synchronization between the two devices in order to allow an active communication to be re-established when needed.
However, the sending of poll packets through a wireless link for a long time is likely to be costly in terms of energy use.
Contactless devices are widely used for authentication. Individuals have a need for a unique contactless device comprising as much authentication information as possible for executing secure electronic transactions, logins on mobile device etc. . . , without having to remember all of them.
The applicant has thus developed personal contactless devices allowing an individual to have in the same device a lot of authentication information, said device being wearable by individuals and having a body-coupled communication interface. The contactless device can be on a bracelet, an ankle, a belt, a garment, in a pocket etc. . .
The authentication is easy to perform for the user. Indeed, when a user, wearing said contactless device, touches (or is close enough) to a device to which the user has to be authenticated, the authentication is performed by the contactless device without any further action than the touching action to be performed by the user wearing the contactless device.
For example, when a user wearing said kind of contactless devices touches the doorknob of a door, said doorknob being able to communicate with the contactless device, it opens said door.
The contactless device communicates through the skin of the user with the device to which the user wants to authenticate. This kind of communication is named body-coupled communication (BCC). The BCC is based on the principle that modulated electric field may carry a signal on a user body according to a capacitive coupling mode, thus the human body, and more particularly the skin, is used as a wire between the contactless device and a device with which it communicates with to ensure authentication of the user.
The contactless device is connected to a proxy and said proxy is connected to a device to which the authentication has to be performed.
The first device is powered by a battery and the second device is fully powered by a power supply.
Usually, the communication between a contactless device and its associated proxy follows the following scheme: the user wearing the contactless device touches the proxy, by this touch the proxy and the contactless device can exchange a secret information through a BCC path, and then a secure wireless communication path, based on this secret information, is established between the proxy and the contactless device to exchange another set of data allowing the authentication of the user wearing the contactless device on the device connected to the proxy. The secret information allows the pairing of the devices.
There are two main use cases of these contactless devices:                short-lived use cases. For example, when the contactless device is used to open a door (or allow an e-payment), it has to authenticate itself (and thus the user wearing the contactless device) only once to allow the opening of the door (or the achievement of the e-payment). Thus, once the other set of data has been exchanged through the wireless communication path, the communication is terminated by closing the path. Hence, the communication between the contactless device and the proxy/the door in this use case is a short-lived one; and        long-lived use cases, for which the wireless communication path has to remain open much longer, for example when the contactless device is used to allow a login on a computer. The proxy is connected to the computer; the contactless device is worn by a user. The proxy emulates a card reader and the contactless device emulates the card to be read, said card comprising authentication information. The reading of the emulated card by the emulated card reader allows the login on the computer and the opening of a secure session. But, the card has to remain in the card reader as long as the user wants to keep its session open on the computer, thus the wireless communication has to remain active as long as the user wants to remain logged on its session.        
Contactless devices are battery-powered devices and as they are aimed to be worn by users, their small size induces low capacity battery. Hence, maintaining the wireless communication between the proxy and the battery-powered contactless device for long-lived use cases is highly energy consuming and reduces consequently the lifespan of contactless devices.